Arc lamp



G. P. HAM

ARC LAMP Filed Sept. 17, 1940 Dec. 10, 1940.

INVENTOR 64/?[7 PH/z/P HH/W ZMWMM W I a I F ATTORNEY.

Patented Dec. 10, 1940 PATENT OFFICE.

ARC LAMP Garnet Philip Ham, 01d Greenwich, Conn, as-

signor to American CyanamidCompany, New York, N. Y., a corporation'ofMaine ApplicatioriSeptemberfi.1940,SerialNo.357.099 1 I zolaim -1 r-This invention relates to are lamps and more particularly to animprovement-in high intensity carbon arc lamps used in blueprinting. 1

In operating the ordinary arc lamps which consist of a glassor quartzvessel containing two carbon electrodes separated by an air gap withcurrent being supplied to the electrodes, 'unburned carbon and metalsalts are ejectedfrom the electrodes and aredeposited on the walls ofthe vessel either by. physical contact or by sublimation, graduallyforming an opaque film. This problem is particularly acute in the caseof highintensity lamps so that if the arc is to be used over longperiods of time with full efficiency, the glass chimney must be cleanedfrom time to time. This is not only troublesome but costly in the caseof lamps'whichare used in blueprinting machines containing vfive'or sixautomatic arc lamps for it interrupts the regular routine. On the 00other hand, if the carbon and sublimed metal salt deposits are allowedto collect on the walls of the vessel, the light intensity of the lampdiminishes rapidly to such an extent that in some cases blue prints showa decreased blue intensity for the same amount of exposure after onlyfour hours operatingtime of the machine. In commercial practice theglobes are cleaned after each days run with soap and a medium abrasivepowder but often this is not suflicient for the inner portions of theglobe may show indications of molten areas which occlude carbonparticles and inorganic salts. Hence such a glass is permanentlyimpaired and cannot transmit its maximum illumination.

The present invention is directed to an improvement in are lamps of thecarbon electrode type which consists in directly removing from the areaof the are any unburned carbon particles and metal salts contained inthe electrodes before they are disseminated or carried upward byconvection currents within the globe and deposited on the walls of theglass container. The manner in which this is accomplished can be morereadily understood by reference to the drawing in whichi Fig. 1 is afront plan View of an arc lamp of the present invention;

Fig. 2 is a sectional view showing in greater detail the means forexhausting unconsumed particles and combustion gases from the arc; and

Fig. 3 is a sectional view showing an alternative exhausting means.

Referring more specifically to the drawing, in Figs. 1 and 2 an openended vessel l of transparent material such as glass or quartz isequipped with suitable closure means 2 and 3.

A carbon electrodel is passed down through .the upper plate 2 andelectrode support ll, properly insulated therefrom by meansof bushing 6,and similarly plate. 3 bears carbon electrode 5 which extends upward inthe globe in direct line with 5 carbon electrode 4, an-arc. gap ofappropriate width being maintained betweenv the two electrodes'by anysuitable adjusting mechanism (not shown).. Current is supplied to theelectrodes by any suitable means (not shown). A hollow 10 tube 1provided with a valve 8 is inserted through plateZand extends "downwardin the vessel until its lower end is adjacent to and in horizontalalignment Withthe tip of the upper positive electrode. The lower orifice9 of the tube is prefer-t :15 ably cuppedrandfiared so that when suctionis appliedfrom without, the combustion gases, together withanyunconsumed particles; are withdrawn from the upper region of the arc.Control is effected through valve 8 so that enough suction -20 isapplied to aspirate from the are substantially all'of'the metal saltsand carbon particles which might otherwise be dispersed and form a filmon the wallsofthe vessel, without substantialdistortion :of the arc fromits normal'position between the electrodes. The preferred location andhorn-shaped construction of the lower opening of the tube is shown ingreater detail in Fig. 2.

In Fig. 3 a modified form of exhausting means to be applied to are lampsis shown which con- 30 sists of a tube In inserted into the lamp throughplate 2, the lower open portion of which is flared to completelysurround and enclose the lower portion of the positive electrodedirectly above the arc. The other parts of the lamp shown in 35 thissection correspond and bear the same reference numerals as those givenin Figs. 1 and 2. The funnel-shape construction of the tube shown inthisfigure causes a circularly uniform withdrawal of exhaust gases,unburned carbon and 40 inorganic matter ejected during operation of thelamp without veering the arc and interfering with light transmission.This is of special iman opaque film on the walls of the vessel.

substantially to carbon monoxide. The flow of gases bearing anynon-gaseous particles ejected from the electrodes, follows the path ofthe arc from the negative to the positive electrode, a portion beingreflected 01f the tip of the upper electrode and the remainder rushingpast. Suction is applied to the exhaust tube placed adjacent to the tipof this upper electrode, or to the funnel as the case may be, and thesegases containing any substances that cause fogging are sucked out andthus are prevented from ever reaching the glass walls.

The suction or reduction of pressure within the exit tube efiectingexhaustion, is accomplished in any manner such as attaching to the endof the tube exterior to the lamp a lowpowered pump or similar devicewhich creates a partial vacuum within the tube. "If the lamp is to beused in a blueprinting machine such as that described in U. S. Patent1,988,593, a constant suction is maintained by means of a fan blowerinstalled to cool the several arc lamps :operating therein. The rush ofair from the fan horizontally across the exterior open end of theinserted tubes is sufiicient to cause a partial vacuum within the tubes;exhaust gases bearing unconsumed particles flow toward this low-pressureregion, and thus film-forming substances are continually swept out ofthe lamp interiors. In other words, the fan blower of the machine isutilized in conjunction with arc lamps of the present invention not onlyto cool the glass or quartz globe which is necessary when the lamps areoperating at high intensities over long periods of time, but also toexhaust combustion gases together with non-gaseous substances whichotherwise would be deposited and form As has been pointed out above,this is of prime 4Q importance in commercial blueprinting processes asit dispenses with periodic cleaning of the individual lamps in themachine and permits continuous operation as well as prolonging the lifeof the arc lamp. While, therefore, any. stand- .45 ard pumping mechanismmaybe used, employment of the fan blower to effect pressure reduction iseconomically preferred when are lamps of the present invention are usedin large-scale blueprinting machines.

The tube or funnel for withdrawing the filmforming particles from thearc flame may be made of quartz, stainless steel, or any other suitablematerial. If stainless steel or other metal is used an insulatingbushing should be provided. HoWever, it is ,not intended to limit thepresent invention to any particular materials of construction nor to thestructural details shown in the accompanying drawing and describedabove, as it may be desirable to employ various modifications dependingon the particular design and use of the arc lamp or lamps if a pluralityare employed, for example in a blueprinting unit.

While the present invention is directed to an improvement in arc lampsgenerally it is particularly important in arc lamps employing coreelectrodes where fogging is especially critical, and the term carbonelectrode used in the specification and claims :is therefore to beconstrued broadly as including vcore electrodes containing othersubstituents in addition to carbon.

What'I'claim is:

1. In an enclosed arc lamp of the blueprint printing type theimprovement Whichcomprises in combination a hollow exhaust .tube one endof which .is positioned adjacent the arc flame, the other opening-beingoutside the lamp enclosure, means co-acting with said exterior openingfor causing reduction .of pressure within said exhaust tube, the size ofthe exhaust tube and the capacity of the 'co-acting'means being suchthatiin normal operation :of the lamp there is no substantial wavering.of the flame.

2. An improved arc lampaccording to claim 1 in which one end of the.hollow exhaust tube is flaredto completely encircle the lower portionof the upper electrode directly above the arc flame, said .flared endbeing provided with a flanged .opening vforming a .sleeve through whichthe electrode Lpasses.

'GARNETPHILIP HAM.

